Cemented carbide rotary tools (i.e., tools driven to rotate) are commonly employed in machining operations such as, for example, drilling, reaming, countersinking, counterboring, end milling, and tapping. Such tools are typically of a solid monolithic construction. The manufacturing process for such tools may involve consolidating metallurgical powder (comprised of particulate ceramic and binder metal) to form a compact. The compact is then sintered to form a cylindrical tool blank having a solid monolithic construction. As used herein, monolithic construction means that the tools are composed of a material, such as, for example, a cemented carbide material, having substantially the same characteristics at any working volume within the tool. Subsequent to sintering, the tool blank is appropriately machined to form the cutting edge and other features of the particular geometry of the rotary tool. Rotary tools include, for example, drills, end mills, reamers, and taps.
Rotary tools composed of cemented carbides are adapted to many industrial applications, including the cutting and shaping of materials of construction such as metals, wood, and plastics. Cemented carbide tools are industrially important because of the combination of tensile strength, wear resistance, and toughness that is characteristic of these materials. Cemented carbides materials comprise at least two phases: at least one hard ceramic component and a softer matrix of metallic binder. The hard ceramic component may be, for example, carbides of elements within groups IVB through VIB of the periodic table. A common example is tungsten carbide. The binder may be a metal or metal alloy, typically cobalt, nickel, iron or alloys of these metals. The binder “cements” the ceramic component within a matrix interconnected in three dimensions. Cemented carbides may be fabricated by consolidating a metallurgical powder blend of at least one powdered ceramic component and at least one powdered binder.
Monolithic rotary tools may additionally comprise coolant channels extending through its body and shank to permit the flow of a coolant, such as oil or water, to the cutting surfaces of the rotary tool. The coolant may enter the channel at the shank end and exit at the drill point. The coolant cools the rotary tool and work piece and assists in ejecting chips and dirt from the hole. The use of coolant during machining operations allows for the use of higher cutting speeds of the rotary tool and faster feed rates, in addition to extending tool life. Rotary tools with coolant channels are especially suited for drilling deep holes in hard materials.
Drilling is a cutting operation in which material is removed from a workpiece to provide a bore in or through the workpiece. Drilling is carried out by advancing a rotating drilling tool or “drill” into the workpiece in the direction of the drill's longitudinal axis. Common drill configurations include, for example, twist drills and spade drills. A twist drill is characterized by one or more helical flutes disposed along at least a portion of the length of the drill and which terminate at a working end of the drill (the “drill tip”), which includes cutting edges. In contrast, a spade drill includes a wide cutting blade at the drill tip and lacks helical flutes along its length. Twist drills have a more complex geometrical design than spade drills due to the helical flutes, and this makes twist drills generally more difficult to manufacture. Twist drills are manufactured as either non-composite twist drills or composite twist drills.
A rotary cutting tool, such as a drill or twist drill, is generally comprised of a cylindrical shaft having at least one flute and land, which follow a helical angle to a forward cutting edge at the forward end of the shaft. The land has associated with it a margin and a clearance portion behind the margin. A side cutting edge is defined by the intersection of the flute with the margin of the land.
A problem that is experienced with a drill during the drilling process when the irregular rotational action of the drill during the drilling process results in an irregular surface structure of the boring wall is commonly known as “chatter.” This phenomenon is because linear or spiral chip flutes are shaped into the generated surfaces of the drills to remove the chips that are formed during the drilling process. Frequently, the chip flutes on one hand and the cutting edges of the drill on the other hand are distributed symmetrically over the periphery of the drill. This symmetrical distribution has the further disadvantage that the vibrations of the drill that cause the “chatter” recur periodically during the drilling process. This periodic recurrence of the vibrations causes an increase in the amplitude of the vibrations, i.e. a “build-up” of the chatter during the drilling process. The result is that the irregularities in the side walls of the hole which is being bored, which irregularities are also called “chatter marks” increase, resulting in a deterioration in the quality of the boring over the length of the drilling process.
To reduce this problem, it is generally known that the minor cutting edges of the drill that are present on the drill periphery can be provided with lands. These lands are generally snug up against the inside wall of the boring and act on the drill in the manner of support fins. An additional measure to prevent the untrue running of the drill is the asymmetrical arrangement of the chip flutes and correspondingly of the drill cutting edges.
The present invention has been developed in view of the foregoing.